He is rolling his shoulder's forward to make himself a smaller target, something Driver's seen in law enforcement when criminals are around the police.

Bowling is a sport in which players attempt to score points by rolling a bowling ball along a flat surface, usually a wooden or synthetic surface, either into pins or to get close to a target ball.

Basically, one set will affect a whole area at once, the direct target spells damage only the enemy target, while the shockwave will have a rolling effect... going outwards to the enemies.